Field of the Invention
The present invention relates to a method for echo compensation in connections in a communications network. A connection is setup from a terminal to an intelligent peripheral through the communications network. The intelligent peripheral is coupled to an access node of the communications network and has an echo control device for providing echo compensation. The communications network has further echo control devices that can be requested if required and can be inserted into established connections in order to suppress any occurring echo signals.
It is known that in communications between persons, echo signals are undesirable in the telecommunication networks if the propagation time of the echo exceeds a certain value.
This is because the echo signals disturb the parties involved in the connection. The echo signals are produced by unavoidable reflections at the 2-wire/4-wire transition in the so-called hybrid and/or by direct acoustic coupling in the subscriber terminal. To reduce or completely eliminate the echo signals in links (connections) with relatively long propagation times, network operators provide echo control devices, e.g. echo suppressors or echo cancellers, which are activated when required and are inserted into the links, in certain switching nodes of the network.
The echo control logic in the switching node decides on the basis of various criteria whether an echo control device must be inserted for a certain link. These criteria are:
a) permanently programmed routing data containing information on the distance (and thus on the propagation time) between an origin and a destination of a link, the echo control device being inserted when a certain distance is exceeded;
b) the propagation time of the useful signal, which is determined dynamically when a connection is set up;
c) information relating to terminal/line (with or without echo source), i.e. information providing a clue on whether or not an echo is produced in a line or terminal; and
d) information relating to the provision of echo control devices which is received from other switching nodes involved in the setting-up of the connection.
In this configuration, the echo control logic in each case attempts to activate an echo control device which is as close as possible to the echo source. The echo control devices can be provided in accordance with International Telecommunication Union (ITU) Recommendation Q.115(97). This recommendation describes where in the network such devices are to be preferably provided and what procedures are to be used for activating them.
The echo problem is different in communications between a person and an intelligent peripheral. Intelligent peripherals are used, for example, in a so-called intelligent network. They are used when a subscriber is using a special service. If, for example, the subscriber wishes to establish an arbitrary connection from an arbitrary location without involving a cash payment, he can first set up a service link and will then be connected to an intelligent peripheral. The intelligent peripheral checks the authorization etc. of the subscriber, then accepts his call request and finally initiates the establishment of the required connection. The fees for the connection are then charged to the current telephone account of the subscriber.
The user communicates with the intelligent peripheral from his terminal by use of voice signals or frequency code signals.
In contrast to the normal voice communication between two subscribers, where an echo only causes interference above a certain propagation time, an echo occurring during the dialog between a subscriber and an intelligent peripheral is an interference factor which impairs the evaluation of the received signals (voice recognition or frequency code recognition) in the intelligent peripheral, independently of its propagation time. A solution for bypassing this problem consists in allowing voice or frequency code information to be input only within certain time windows during the dialog with the intelligent peripheral, i.e. the dialog of a subscriber with the intelligent peripheral is carried out in a half duplex mode. This solution allows for a simpler construction of the intelligent peripheral since it does not require any measures for echo control. However, carrying out a dialog in the half duplex mode is cumbersome and time consuming for practiced users, especially if the announcement texts output by the intelligent peripheral are multilingual and/or if the signal propagation times are long, as is the case with long links (e.g. satellite links). Moreover, the resources are in use for relatively long time intervals, which is why this solution is only suitable for automatic information service machines which are dialed up via special service codes, or for answering machines.
In the solution where, in contrast, a normal, i.e. natural, dialog, if possible, is required, an echo control function must be provided for the intelligent peripheral. In this configuration, the intelligent peripheral itself can be equipped with an echo control device or an echo control device can be allocated to it permanently or on request in its network access node. In the text that follows, the two cases (control device disposed in the intelligent peripheral or allocated to the intelligent peripheral) will be called xe2x80x9cownxe2x80x9d echo control. This solution is more user-friendly and the relevant resources are only in use for as long as they are actually needed. Moreover, the connection set-up time is shorter in comparison with the first-mentioned solution. However, these advantages must be paid for with a more complex equipment level of the intelligent peripheral or of its access node, respectively. In addition, the echo propagation time compensation of the echo control device of the intelligent peripheral cannot be configured to be of any arbitrary size since otherwise the expenditure for the components required for this (memory, high-performance computer) becomes disproportionately high.
It is accordingly an object of the invention to provide a method for providing echo control devices in communication links to intelligent peripherals that overcome the above-mentioned disadvantages of the prior art methods and devices of this general type, which is effective in every case and requires relatively little expenditure.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for providing echo compensations, which contains the steps of setting up a connection from a terminal to an intelligent peripheral through a communications network. The intelligent peripheral is coupled to an access node of the communications network and has an echo control device for providing echo compensation. The communications network has further echo control devices that can be requested if required and can be inserted into established connections in order to suppress any occurring echo signals. Subsequently, in the access node, a signal propagation time vlz of the connection from the terminal to the intelligent peripheral is compared with a value of an echo propagation time cancellation elk of the echo control device of the intelligent peripheral. An information item is output into the communications network to request an addition of one of the further echo control devices in the communications network if the condition vlz greater than xc2xd elk is met.
The method according to the invention exhibits the advantage that echo signals occurring in links to the intelligent peripheral are suppressed even when the echo control of the intelligent peripheral is not sufficient. In such a case, additional devices for echo control, if available in the network, are utilized in dependence on the echo control device of the intelligent peripheral and in dependence on the signal propagation time of the link. For this reason, the expenditure for the echo control device of the intelligent peripheral echo control can be limited. The method guarantees echo suppression in every case independently of the geographic extent of the communication network or of the value of the signal propagation times occurring therein.
In accordance with an added feature of the invention, there are the steps of deriving a signal propagation time vlze from the equation:
vlze=vlzxe2x88x92t1,
where t1 is the signal propagation time between the terminal and an echo source in a further access node of the communications network associated with the terminal. In the access node for the intelligent peripheral, the signal propagation time vlze is compared with the value of the echo propagation time cancellation elk of the intelligent peripheral; and the information item is output into the communications network in order to request an addition of one of the echo control devices available in the communications network if the condition vlze greater than xc2xd elk is met.
In accordance with an additional feature of the invention, there is the step of deriving the signal propagation time vlze by transmitting separately a value of the signal propagation time t1 and then subtracting the value of the signal propagation time t1 from the signal propagation time vlz in the access node for the intelligent peripheral.
In accordance with another feature of the invention, there are the steps of acquiring and deriving in the access node for the intelligent peripheral both the signal propagation time vlz and the signal propagation time vlze.
With the foregoing and other objects in view there is further provided, the combination of a terminal and an intelligent peripheral having an echo compensation device generating an echo propagation time cancellation signal elk, with a system for providing echo compensation in a connection between the terminal and the intelligent peripherals. The system contains a communications network connecting the terminal to the intelligent peripheral. The communications network has further echo control devices and switching nodes connected to the further echo control devices. The switching nodes include a first access node for connecting to the intelligent peripheral and a second access node for connecting to the terminal. The further echo control devices can be requested when required and can be inserted into established connections in order to cancel any echo signals which occur. The first access node for the intelligent peripheral has an echo control logic for performing a comparison between one of a first signal propagation time vlz and a second signal propagation time vlze and the echo propagation time cancellation signal elk of the intelligent peripheral. The echo control logic can request that one of the further echo control devices be available if one of vlz greater than xc2xd elk and vlze greater than xc2xd elk is met.
In accordance with a concomitant feature of the invention, the first access node has a propagation delay counter for registering the signal propagation time vlz and a further propagation delay counter for registering the signal propagation time vlze, and propagation time values required for determining the signal propagation time vlz and the signal propagation time vlze can be transmitted to the switching nodes involved in a connection by use of a signaling protocol.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for providing echo control devices in communication links to intelligent peripherals, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.